Welding

SectionSectionSection

2

Chapter 5: SMAW: Equipment and Supplies

Chapter 6: SMAW: Equipment Assembly andAdjustment

Chapter 7:SMAW: Electrodes

Chapter 8: SMAW: Flat Welding Position

Chapter 9:SMAW: Horizontal, Vertical, and Overhead Welding Positions

Chapter 10:Surfacing

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51Chapter 5 SMAW: Equipment and Supplies

ChapterChapterChapter 5

SMAW:Equipmentand Supplies

SMAW:SMAW:Equipmentand Suppliesand Supplies

After studying this chapter, you will be able to:

Describe the differences between direct current(dc) and alternating current (ac).

Interpret American Welding Society (AWS)abbreviations regarding welding current polarity.

Identify the equipment and accessories used inshielded metal arc welding (SMAW).

Identify factors to consider when selecting an arcwelding machine.

Shielded Metal Arc WeldingPrinciples

Shielded metal arc welding (SMAW) is a weld-ing process in which the base metals are heated tofusion or melting temperature by an electric arc. Thearc is created between a covered metal electrode andthe base metal. A shielding gas protects the basemetals, arc, electrode, and weld from the atmos-phere during welding. The shielding gas is createdas the flux covering on the electrode melts. Whenthe flux solidifies, it forms a protective slag over theweld bead. The melting electrode wire furnishesfiller metal to the weld. See Figure 5-1.

alternating current (ac)bridge rectifierchipping hammerconstant current (CC)constant voltage (CV)cover platecyclediodedirect current (dc)

direct current electrode negative (DCEN)

direct current electrode positive (DCEP)

direct current reverse polarity (DCRP)

direct current straight polarity (DCSP)

droop curve machines

TechnicalTerms

bjectivesLearning droopersduty cycleelectrode holderelectrode leadfilter lensflash gogglesfrequencygauntlet gloveshelmethertzinput powerinverterlugopen circuit voltage (OCV)polarityprimary current

rated output currentsecondary currentshielding gasshielded metal arc

welding (SMAW)silicon-controlled

rectifierslagstep-down transformerterminalsvoltage dropwelding outfitwelding stationwire brushwork boothworkpiece lead

This sample chapter is for review purposes only. Copyright The Goodheart-Willcox Co., Inc. All rights reserved.

The temperature of the arc in SMAW can be over9000F (5000C). With the correct diameter electrode,the heat created by the arc is enough to melt anyweldable metal. Mild carbon steel melts at slightlyabove 2800F (1540C).

Shielded metal arc welding is used to constructbuildings, ships, truck chassis, pipelines, and otherweldments. SMAW equipment is fairly inexpensive. Itis widely used on farms and in small repair shops.

SMAW Current and PolarityIn SMAW, electrical current flows across an air

gap between the covered electrode and base metal. Anelectric arc is formed as the current flows across theair gap. The arc creates the heat required for welding.

The electrical current for welding is supplied byan arc welding machine. Welding machines, alsocalled power sources, produce two types of current:direct current (dc) and alternating current (ac).

An electrical current is actually the flow of elec-trons within a circuit. The direction that the electronsflow is referred to as the polarity. Electrons flow froma negatively charged (polarized) body to a positivelycharged body. Direct current may flow from the electrode to the base metal. When the current flows in this direction, the electrode has negative polarityand the base metal has positive polarity. It is called

direct current electrode negative (DCEN). Direct currentelectrode negative is also known as direct currentstraight polarity (DCSP). See Figure 5-2. The currentdirection may be reversed to flow from the base metalto the electrode. When the current flows in thisdirection, the base metal has negative polarity, and theelectrode has positive polarity. It is called direct currentelectrode positive (DCEP). Direct current electrodepositive is also known as direct current reverse polarity(DCRP). See Figure 5-3.

The direction selected is determined by themetal thickness, joint position, and type of electrodeused. The selection of polarity is covered later inthis chapter.

Welding Technology Fundamentals52

Electrodewire

Direction

of travel

Shieldinggas

Arc flame Slag

Base metal

Depth ofpenetration

Fluxcovering

Welding arc

Weld pool

Figure 5-1. In shielded metal arc welding, slag covers the weldbead while it cools. Shielding gas is formed as the flux coveringis burned.

Electrodeholder

Electrode()

Arcgap

Workpiece(+)

Figure 5-2. A diagram for a direct current electrode negative(DCEN) arc welding circuit. Notice the current is travelingfrom the negative electrode to the positive base metal.

Electrodeholder

Electrode(+)

Arcgap

Workpiece()

Figure 5-3. A diagram for a direct current electrode positive(DCEP) arc welding circuit. In DCEP, the current travelsfrom the negative base metal to the positive electrode.


Direct CurrentDirect current (dc) flows in only one direction.

Current flows from one terminal of the weldingmachine to the base metal. It then flows back to thesecond terminal of the welding machine. On somewelding machines, the electrical leads are manuallyreversed on the machine terminals. This changes thedirection of current flow. On other machines, a polar-ity switch is flipped to electrically reverse the terminalleads within the machine. See Figure 5-4. Weldingmust be stopped and the electrode insulated fromthe circuit whenever the polarity is changed.

The circuit polarity affects the selection of the cov-ered electrode and how the covered electrode willperform. Direct current electrode positive (DCEP)used with the proper electrode produces deeper pen-etration than direct current electrode negative(DCEN). Most electrodes use DCEP.

Direct current electrode negative (DCEN) is usedwith electrodes that do not produce deep penetration.A small electrode using DCEN and a low-current settingwill produce a soft arc with only minimal penetra-tion. Thus, DCEN, with proper electrodes, is used forwelding thin metals. DCEN is also used with someelectrodes to deposit weld metal quickly. DCEN canmelt an electrode more rapidly and deposit fillermetal at a faster rate than DCEP.

When limited to a certain polarity, the selection ofthe electrode will depend on the type of polarity. Ifonly certain electrodes are available, the electrode willdetermine the type of polarity. The polarity and theelectrode must always agree.

Alternating CurrentAlternating current (ac) generally operates at 60

cycles per second in the United States. A cycle is a setof repeating events, such as the flow and reversal offlow in an electrical circuit. Alternating current flowsin one direction for 1/120 of a second, then reversesits direction and flows for 1/120 of a second to formone complete cycle. See Figure 5-5. The total time fora cycle is 1/60 of a second:

1/120 sec + 1/120 sec = 1/60 secFrequency is a term used to describe the number

of cycles per second there are in ac power. Frequencyis measured in hertz (Hz). One cycle per second is thesame as one hertz. Thus, ac power at 60 cycles per sec-ond is also called 60-hertz power.

Welding with ac and with ac electrodes producesa medium depth of penetration. Many electrodes (butnot all) will work with alternating current. SeeChapter 7 and manufacturer's recommendations formore information on electrodes.

SMAW OutfitSMAW requires the use of proper protective

clothing and various tools, supplies, and equipment.The welding outfit includes equipment required toactually create a weld. The welding station includestools, supplies, and other items required to makewelding safe and comfortable. A complete SMAWoutfit includes the following: Welding machine/power source (dc, ac, or ac/dc).

Electrode and workpiece leads.

Electrode holder.

Selects alternatingcurrent

Selects direct currentelectrode positive

Selects direct currentelectrode negative

Figure 5-4. This polarity switch has positions for DCEP, AC,and DCEN.

Maximum

Curre

nt

1/120 sec

1/60 secOne cycle or hertz (Hz)

Time

Maximum

00

1/120 sec + 1/120 sec = 2/120 sec = 1/60 sec

Figure 5-5. Alternating current plotted against time results inan ac sine wave. The current increases from zero and returns tozero. It then increases in the opposite direction and returns tozero. The complete process is one cycle and takes 1/60 second.

A complete SMAW station, Figure 5-6, includesthe SMAW outfit plus the following: Ventilation.

Welding table.

Welding booth with an opaque (solid) or filteredtransparent plastic screen.

Covered electrodes.

Chipping hammer and wire brush.

Arc Welding MachineArc welding machines produce either a constant

current (CC) or a constant voltage (CV). Manualwelding processes, such as SMAW, require a constantcurrent (CC) welding machine. If a CC weldingmachine is not used, large changes in current occurwhenever a welder changes the arc length slightly.

Since it is impossible to manually maintain a constantarc length without any variation, a CC weldingmachine is used.

CC welding machines are also called droopers ordroop curve machines. This name is derived from thevoltage versus amperage curve produced by themachines. Figure 5-7 shows the curve shape for a CCwelding machine.

Examine Figure 5-7 closely. An increase from 20volts to 25 volts is a 25% increase in voltage. Thischange in voltage results in an increase in currentfrom 125 amps to 130 amps, only a 4% increase. If thewelder varies the arc length, it causes a change in volt-age. However, the amperage changes very little witha CC welding machine. Although the current variesslightly, these welding machines are considered con-stant current. Both ac and dc welding machines areavailable as constant current machines.

Selecting an Arc Welding MachineAc welding machines meet most welding require-

ments. They are easy to use and generally cost lessthan comparable dc welding machines. Therefore,they are widely used on the farm and in the homeshop. See Figure 5-8.

Because the polarity can be changed, dc weldingmachines are more versatile than ac machines. Theability to change the polarity allows the welder tomake out-of-position welds and to weld thin metalmore easily. It also allows the welder to vary the heatapplied to the metal. DCEP provides deep penetrationfor welds on thick metal; DCEN deposits filler metalfaster. DCEN is used more easily on thin metal.

Some arc welding machines are combinationac/dc machines. These machines can be used as acwelding machines and then can easily be switched to


Figure 5-6. This is a well-equipped shielded metal arc weldingstation.

Volts

8070605040302010

00 25 50 75 100 125 150 175 200

Amperes

Figure 5-7. A volt-amp diagram for a constant currentmachine. The constant current (CC) welding machine is calleda drooper because of this curve. A 25% change in voltageresults in only a 4% change in amperage. The current changeis so slight that the current is considered constant.


dc welding machines. Combination machines have agreater flexibility in their use. However, they are moreexpensive than ac or dc machines.

Machine designs can be different types. The mostcommon are: Transformerused for ac.

Transformer-rectifierused for ac and dc.

Inverter power supplyprovides ac and dcoptions.

Motor generatorused to create dc power.

Motor alternatorused to create ac power; withaddition of a rectifier, can produce dc power. SeeFigure 5-9.The function of a power supply is to take the high-

voltage, low-current supplied power and change itinto the low-voltage, high-current power needed forwelding. Welding transformers are called step-downtransformers because the voltage is reduced.

Alternating current is supplied to one side of atransformer. This is called the primary current. The cur-rent coming out of the transformer, which is used forwelding, is called the secondary current. Alternatingcurrent is used as the input to the transformer. Theoutput of the transformer is also alternating current,but at a higher amperage and lower voltage.

To obtain direct current, the alternating current is passed through a set of diodes or silicon-controlled

rectifiers (SCRs). Diodes and silicon-controlled rectifiersare electrical devices that allow current to flow in onlyone direction. (Remember, alternating current flows intwo directions.) A bridge rectifier is a group of diodes orSCRs used to transform ac into dc. Figure 5-10 shows abridge rectifier circuit.

Another type of power supply is an inverter.Inverter machines are very small and lightweight.

Current rangeselector

Current adjustmentdial

Figure 5-8. An ac shielded metal arc welding machine has twocurrent ranges. The desired current is set by selecting a current range and setting the desired current using the adjustmentdial. (Miller Electric Mfg. Co.)

Generatorengine

AC/DCpolarityswitch

Figure 5-9. A portable engine-driven ac/dc welding powersource has a switch used to select ac or either dc polarity.(Lincoln Electric Company)

Transformer

Inductor

SCR SCR

SCRSCR

Controls

+

Figure 5-10. This is a bridge rectifier that uses SCRs tochange ac current into dc current. SCRs conduct current inonly one direction.

An inverter power supply uses electrical circuits tochange the input frequency to the transformer. SeeFigure 5-11.

First, an inverter machine takes single-phase orthree-phase power and passes it through a bridge rec-tifier. This creates dc current. Next, this dc current ischopped into very high-frequency ac current. The fre-quency can be between 1,000 and 50,000 cycles persecond or 1kHz to 50kHz (the k means 1000). Thishigh-frequency current is passed through a small, effi-cient transformer. Low-voltage, high-current poweruseful for welding is produced. This power still has avery high frequency. Another bridge rectifier and aninductor are used to create smooth dc output. Inverterpower supplies can be used for all arc weldingprocesses and for plasma arc cutting.

Some welding machines taken to job sites whereno electricity is available have a gasoline or dieselengine as the power supply. The engine turns a gen-erator or alternator. These create dc and ac power,respectively.

After selecting an ac, dc, or ac/dc machine, thefollowing variables must also be considered: Input power requirements.

Rated output current rating.

Duty cycle.

Open circuit voltage.Input power requirements. Welding machines

used in school shops, trade schools, and industry areconnected to commercially available electric power.Power requirements for a welding machine must bespecified to the electrician when the machine is wiredinto a building. The input power of a welding

machine must correspond with the type of power thatis available. It is fairly expensive to rewire existing120V power to 240V or 440V.

The input voltage to a welding machine may be120V, 240V, 440V or higher. These high voltages arereduced by a transformer within the welding machineto the required welding voltage. Welding voltageranges from 5V to 30V.

Engine-driven welding machines are used in thefield for pipelines, construction, and other weldingoperations where electric power is not available.Engines are connected to the welding machine to turnan alternator for ac welding current or a generator fordc welding current.

Rated output current. A nameplate on each weld-ing machine shows the rated output current. SeeFigure 5-12. A welding machine must be able to sup-ply the current required for the welds being made.The rated output current depends on the duty cycle.

Duty cycle. The duty cycle is a rating that indi-cates how long a welding machine can be used at itsmaximum output current without damaging it. Dutycycle is based on a ten-minute time period. A weldingmachine with a 60% duty cycle can be used at its max-imum rated output current for six out of every tenminutes. The welding machine may overheat if theduty cycle is exceeded. At lower current settings, theduty cycle may be increased and the power sourceused for a longer period of time.

A duty cycle chart should be provided with a newwelding machine. In Figure 5-13, the duty cycle is20% at the maximum rated output current of 200amperes (A). The duty cycle is 100% at a rated outputcurrent of 100A.


Input bridgerectifier

1- or 3-phaseprimary

Output bridgerectifierInverter Inductor

+

-

Transformer

Invertercontrolcircuit

Figure 5-11. An inverter power supply takes a number of steps to change the supplied power into power used for welding. Thedifferent steps and the resulting waveform are illustrated.


Open circuit voltage. Welding machines have amaximum voltage, or open circuit voltage. Open circuitvoltage (OCV) is the voltage of the welding machinewhen it is on, but is not being used. The maximumOCV for most manual ac or dc machines is 80V.This relatively low OCV protects workers fromelectrical shock. The 80V OCV is still high comparedto the 5V-30V closed circuit welding voltage. AnOCV of 80V is required to start the arc easily. It is alsonecessary to maintain the arc during ac welding.

Welding LeadsThe electrical cable that connects the electrode

holder to a welding machine is the electrode lead. Theworkpiece lead (ground) is the electrical cable thatconnects the base metal to the welding machine.

On large welding machines, leads may berequired to carry 600A or more. Leads must have alarge diameter to carry such high current. They mustalso be flexible so a welder can easily move them. Asmany as 2500 fine conductors are used in a weldinglead to produce the flexibility required. Welding leadsmust also be well insulated to prevent electricalshock. They are usually insulated with a heavy rubberor neoprene covering. See Figure 5-14.

Voltage and current are affected when the weldingleads are the wrong diameter. Electrical resistance inthe lead increases as its diameter decreases or itslength increases. Voltage drop (voltage loss) occurswhen electricity travels a long distance from the weld-ing machine. A larger diameter lead is used to coun-teract the voltage drop when long leads are required.A greater amount of current flows in a larger diameterlead when voltage drop is held to a minimum.

Figure 5-12. Rated output information is often shown onwelding machines. During ac operation, the output is 250amperes at 30 volts. In dc, the output is 200 amperes at 28volts.

Rated Duty Cycle300

250

200

150

10015 20 30 40 50 60 70 80 90 100

We

ldin

g Am

pere

s

% Duty CycleFigure 5-13. Duty cycle versus welding current graphsshould be provided with each new arc welding machine. Theduty cycle for this machine is 20% at 200A. At 100 amperes,the machine may be used 100% of the time.

Figure 5-14. This arc welding lead shows the large number offine copper wires used. When twisted into larger bundles,these fine wires give the lead its flexibility. The lead is thencovered with insulating material, cord reinforcement, and anouter layer of rubber or plastic.

Welding leads are available in a variety of diame-ters. The diameter is referred to by number size. Thesenumber sizes and their actual diameters are shown inFigure 5-15. Figure 5-15 also shows what size leadshould be used to carry a given amperage to the weld-ment and back. The amperages shown are the maxi-mum that can be carried in the various leads over thestated distances.

Lead ConnectionsWelding leads are connected to the welding

machine and base metal with lugs, clamps, or specialterminals. Figure 5-16 shows several lugs that may beused on the machine end of the workpiece and elec-trode leads. Lug connections can also be used to con-nect the workpiece lead to the welding table. Specialpush-and-turn connectors are shown in Figure 5-17.These quick-connect terminals may be used on bothwelding leads.

Various other types of clamps or special connec-tors may be used to connect the workpiece lead to thebase metal. The workpiece lead may be clamped tothe base metal using a spring-loaded clamp, as shownin Figure 5-18. Occasionally, a part must be weldedwhile it is being rotated. A special rotating workpiececlamp is used for this application, Figure 5-19. Lugs,spring clamps, or other special connectors aremechanically connected or soldered to the bare end ofthe leads.

Electrode HolderThe electrode holder is held by the welder during

the welding operation. The well-insulated handle of

the electrode holder protects the welder from electri-cal shock. An electrode is clamped in the copper alloyjaws of the electrode holder. The jaws provide a goodelectrical contact for the electrode. See Figure 5-20.The electrode lead is clamped into the electrode holder.The cable clamp is under the insulated handle.

Protective ClothingPockets on shirts, pants, or coveralls should be

covered to prevent sparks from being caught inthem. The top collar button should be fastened,especially when welding out of position. Pant legsshould not have cuffs.

A cap should be worn to protect your hair. Leathergloves should be worn. Gauntlet gloves, leather gloveswith long cuffs, are the type preferred for out-of-positionwelding. High-top shoes offer added safety from sparks.Steel-toed shoes are recommended when workingaround heavy metal parts.


Welding Lead Current Capacities

Lead Number Lead Diameter Length Length Length0 50 ft.

0 15.2 m50 100 ft.

15.4 30.5 m100 250 ft.30.5 76.2 m

in. mm Amperage Amperage Amperage

4/03/02/01/01234

.959

.827

.754

.720

.644

.604

.568

.531

24.421.019.218.316.415.314.413.5

600500400300250200150125

600400350300200195150100

400300300200175150100

75

Note: Lengths given are for the total combined length of the electrode and work leads.

Figure 5-15. Welding lead size recommendations. Lead sizes range from 4/0 to 4. If the work is 100 (30.5 m) from the machine,200 (61 m) of leads are needed: 100 (30.5 m) for the workpiece lead and 100 (30.5 m) for the electrode lead. Size 1/0 leads arerequired to carry 200A through 200 (61 m) of leads.

Figure 5-16. These lugs are for arc welding leads. They areusually connected to the lead by means of a mechanical crimp.(Lenco)


A

B

C

D

E

F

Figure 5-17. ACThese are all examples of European con-nectors called DIN connectors. Each connector has a smallraised square on the round shaft. DIN connectors are mostoften used for making lead connections. DThis DIN con-nector also has a gas connection. EThis is an American-typeconnector, which has a split round shaft. FAn American toDIN adapter. (Lenco)

Figure 5-18. Two types of spring-loaded workpiece lead clamps.(Lenco)

Figure 5-19. This rotating workpiece lead connector has socketsfor four workpiece leads. (Lenco)

Jaws Handle

Setscrew secureslead in place

Release lever

Figure 5-20. This SMAW electrode holder has its insulatedhandle slid back to show the lead connection. An electrode isheld tightly in the jaws by pressure from a heavy coil springunder the release lever.

Arc Welding Helmets and LensesAn electric arc creates ultraviolet and infrared

rays. These light rays are harmful to the eyes andcause burns, like sunburn, on bare skin. A weldershould cover all bare skin areas while welding.

An arc-welding helmet serves several purposes. Itshields the face and neck from the harmful rays andprotects these areas from molten metal that may spatterfrom the weld area. The filter lens and cover plate arealso held by the helmet. A #10#14 filter lens shouldbe used for SMAW. A darker lens is required as theelectrode diameter increases. See Figure 5-21. Filterlenses must conform to the American NationalStandards Institute standard Z87.1, which covers therequirements for welding eye protection.

Many filter lenses are auto-darkening. When thereis no arc, an auto-darkening lens allows you to viewthe weld area and position the electrode. The auto-darkening lens senses the arc and immediately(1/12,000th to faster than 1/20,000th of a second orfaster) darkens to the preset lens shade number. Manyauto-darkening lenses are variable and can be set todifferent shade numbers.

Some welders use a fixed shade lens. When weld-ing, the helmet is flipped down over the face with a nodof the head. When welding is completed, the helmet islifted up. Figure 5-22 shows both types of helmets.

Clear plastic or glass cover plates protect the filterlens from arc spatter. Always use cover plates. One isused in front of the filter lens and one behind the fil-ter lens. Filter lenses and especially auto-darkeningfilter lenses are more expensive than cover plates andshould be protected. Replace cover plates regularlywhen they get scratched or speckled with spatter.

Filter lenses and cover plates are available in twosizes: 2 4 1/4 (51 mm 108 mm) and 4 1/2 5 1/4(114 mm 133 mm). An arc-welding helmet can beadjusted for various head sizes. Adjustable screwssecure the headband to the helmet. These screwsshould be tight enough to prevent the helmet fromfalling down when it is raised. However, the helmetshould fall into position over the face when thewelders head is nodded.


Application Lens ShadeNumberSMAW (Shielded metal arc welding)Up to 5/32 in. electrodes3/16 - 1/4 in. electrodes5/16 - 3/8 in. electrodes

GMAW (Gas metal arc welding)(nonferrous)Up to 5/32 in. electrodes

GMAW (Gas metal arc welding)(ferrous)1/16 - 5/32 in. electrodes

GTAW (Gas tungsten arc welding)

101214

11

12

10 to 14

Figure 5-21. The suggested filter lens shade numbers for variousarc welding applications.

Figure 5-22. AA fiberglass helmet with a large passive orfixed shade. BThe auto-darkening filter lens in this helmethas a variable shade setting. (Jackson Safety, Inc.)

A

B


Arc welders often wear flash goggles under theirhelmets. Flash goggles protect the welders eyes fromflashes from the rear. A #1#3 lens is often used inthese goggles.

VentilationAdequate ventilation must be provided when

performing any type of welding. The size or capacityof the ventilation system for a given area should becalculated by a safety engineer.

Exhaust fumes from an arc welding area can betoxic to a welder. A flexible exhaust pickup tube isoften used to remove the fumes. The welder posi-tions the pickup tube for maximum performance.Fumes should be picked up and exhausted beforethey cross the welders face. See Figure 5-23.

Work Booth and TableThe welding table is part of the arc welding sta-

tion. The workpiece lead may be bolted to the tablewith a lug or attached to the table with a springclamp. A weld positioner may be welded or clampedto the table. A shop-fabricated weld positioner isshown in Figure 5-24.

Welding may be done in a work booth or in anopen area. In either case, the electric arc must beshielded from the view of the workers who are notwearing eye protection. Solid walls, canvas curtains,or filtered, transparent plastic may be used. Filtered,transparent plastic curtains must filter more than99% of the ultraviolet and infrared rays from theelectric arc. See Figure 5-25.

Chipping Hammer and Wire BrushSlag must be removed after each arc weld bead or

weld pass is completed. Slag is the hard, brittle materialthat covers a finished shielded metal arc weld. The nextweld bead will have slag trapped in it if the previousweld bead is not cleaned thoroughly. Slag is chippedaway using a chipping hammer. See Figure 5-26.

After chipping the slag, the weld bead is furthercleaned using a wire brush. The bristles of the brushare steel. See Figure 5-27. A wire brush is sometimescombined with a chipping hammer. A rotary wirewheel in a portable electric drill motor may also beused to clean the weld. Always wear goggles whenchipping or wire brushing the slag from a weld.This will help to prevent eye injuries.Figure 5-23. This welder is using a welding fume exhaust sys-

tem. The flexible duct allows the welder to position the pickupvent close to the weld area. (Nederman, Inc.)

Figure 5-24. A fixture used to hold weldments for out-of-positionwelding. This fixture is adjustable in three ways. A C-clampholds the weldment.

Figure 5-25. The curtains in this work area are a filtered, trans-parent plastic. Note also the flexible fume exhaust system.(Nederman, Inc.)


Figure 5-26. The chisel end of a chipping hammer being usedto remove the slag from a finished SMAW weld.

Figure 5-27. A wire brush is used to clean the weld after slaghas been removed.

Shielded metal arc welding (SMAW) is a welding process in which the base metals are heated to fusionor melting temperature by an electric arc. The arc is created between a covered metal electrode and thebase metal. The shielding gas is created as the flux covering on the electrode melts. The flux solidifiesand forms a slag that protects the weld metal while it cools. The melting electrode wire furnishes fillermetal to the weld.

When direct current flows from the electrode to the base metal, it is referred to as direct current electrodenegative or direct current straight polarity.

When direct current flows from the base metal to the electrode, it is referred to as direct current electrodepositive or direct current reverse polarity.

Direct current flows in only one direction. Alternating current reverses direction at a set frequency, usually 60 cycles per second.

A welding outfit consists of the equipment required to actually create a weld. A welding station alsoincludes tools, supplies, and other items required to make welding safe and comfortable.

Arc welding machines used for SMAW produce a constant current (CC).

The electrical cable that connects the electrode holder to a welding machine is the electrode lead. Theworkpiece lead (ground) is the electrical cable that connects the base metal to the welding machine.

A #10#14 filter lens should be used for SMAW. A darker lens is required when using larger diameterelectrodes.

SummarySummarySummary


Write your answers on a separate sheet of paper. Please do not write in this book.

1. Identify the parts of this SMAW in progress.

2. Which electrode polarity should be used when welding thin metals?3. Current that travels from the electrode to the base metal is known as _____ or _____.4. Ac electrodes provide _____ penetration when used for SMAW.5. List eight items found in an SMAW station.6. What do the letters CC and CV stand for? Is a drooper a CC or CV welding machine?7. Refer to Figure 5-13. The duty cycle for this welding machine at 125 amperes is _____%.8. Refer to Figure 5-15. A #_____ electrode lead and workpiece lead should be used to carry 150 amperes

of electricity 75 feet to the workpiece and 75 feet back to the welding machine.9. The temperature of an electric arc in SMAW can be over _____F (_____C).

10. What is the OCV of most manual ac and dc welding machines?

? QuestionsReview

A

Direction

of travel

C

G

D

F

B

H

E


A welder using the SMAW process on a large weldment. Note how the flexible exhausttube is positioned to effectively remove fumes. (Nederman, Inc.)

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